Subsurface safety valves (SSVs) which incorporate a closure member which pivots 90.degree., also known as a flapper, have been in use for many years. Typically, the flapper is pushed downwardly by a tube to get it out of the way of the flowpath. The tubular that pushes the flapper out of the way is known as the flow tube. The flapper is typically spring loaded, such that when the flow tube is pushed or otherwise urged upwardly away from the flapper, the torsion spring or springs bias the flapper 90.degree. to close the flowpath as the flapper engaged a mating seat.
Prior art designs for return springs on flappers are illustrated in FIGS. 1 and 2. FIG. 1 illustrates a flapper 10 which has dual hinges 12 and 14, which are secured by a pin 16 to the body 18 of the SSV. A torsion spring 20 has an annular shape and the pin 16 extends through it as well as through the hinges 12 and 14. A tab 22 comprises the end of the torsion spring 20 and bear on the flapper 10. At the opposite end of the spring 20, another tab 24 is braced against the body 18. When the flow tube (not shown) is pushed down, the torsion spring 20 winds up as the flapper 10 is pushed down through an arc of 90.degree. to get it out of the way so that flow of fluids can occur through the flow tube. When the flow tube is allowed to move upwardly, the spring 20, acting through tab 22, initiates the reverse movement through an arc of 90.degree. of the flapper 10 so that the flapper 10 closes against its mating seat (not shown). One of the problems with this design is limitation of space, which in turn forces the use of fairly high stresses in the springs, such as 20, when used in SSVs. The design of FIG. 1 also has limitations on the closure force available due to the space requirements for fitting the spring between two hinges 12 and 14. Indeed, some designs do not accommodate the use of dual hinges 12 and 14 and, in those instances, the torsion springs have been disposed circumferentially around the periphery of the flapper, as is more clearly illustrated in FIG. 2.
FIG. 2 is another prior art design that involves a flapper 26 which has a single hinge 28. A pin 30 extends through hinge 28 to support the flapper 26 for 90.degree. rotation. Pin 30 has passages or openings 32 and 34 on opposite ends thereof. A pair of torsion springs 36 and 38 are disposed circumferentially adjacent the periphery of the flapper 26. On one end, the torsion springs 36 and 38 are respectively connected to the body 40 of the SSV at connections 42 and 44. At the other end of torsion springs 36 and 38, there are hooks 46 and 48. Hooks 46 and 48 extend respectively through openings 32 and 34. Accordingly, when the flapper 26 is pushed downwardly by the flow tube (not shown), the springs 36 and 38, because of their connections through openings 32 and 34 to the pin 30, resist such movement and coil up to store a closing force. Pin 30 rotates with flapper 26, thus rotating the hooks 46 and 48 as the flapper 26 reaches the fully open position of the SSV. One of the potential problems with this design is the multi-axial movement of the hook ends 46 and 48 in openings 32 and 34. This results in excessive friction and wear of the hook ends 46 and 48, with the possibility of a fatigue failure adjacent the point where the hook ends 46 and 48 enter or exit the openings or passages 32 and 34. This multi axial movement coupled with the multiple interfaces between the flapper and torsion springs can result in excessive play between the torsion spring hook ends, pin and flapper. During the rotation of the flapper and pin, the multi-axial movement of the hook ends can create excessive friction. This friction, combined with the excessive play in the system, can negate some of the force that is stored in the torsion springs.
Accordingly, the objective of the present invention is to facilitate the use of the wrap around style of torsion springs, such as 36 and 38, while at the same time providing an improved torsional loading point which supports the flapper so that excessive play and friction is eliminated.
Accordingly, the objective of the present invention is to facilitate the use of a wraparound style of torsion springs, such as 36 and 38, while at the same time providing an improved connection to the pin which supports the flapper so that concentrated zones of high stress are eliminated and the likelihood of fatigue failure is also severely reduced, if not completely eliminated.
Accordingly, alternative proposals are described to accomplish the objective as will be apparent to those skilled in the art from a review of the description of the preferred embodiments of the invention.